KR100405091B1 - Diagnostic device of exhaust gas purification device for internal combustion engine - Google Patents

Abstract

[Object] In an exhaust gas purifying apparatus for an internal combustion engine having a plurality of catalysts, an air-fuel ratio sensor is provided before and after each catalyst, and the correlation between output signals of air-fuel ratio sensors before and after each catalyst is examined. And each of the catalysts can be diagnosed individually by performing the respective diagnoses in different operating regions.

[Configuration] A plurality of exhaust gas purifying catalysts are provided in an exhaust passage of an internal combustion engine, and a first air-fuel ratio sensor is disposed upstream of the upstream catalyst, a second air-fuel ratio sensor is disposed between the upstream catalyst and the downstream catalyst, Fuel ratio sensor is provided downstream of the downstream catalyst and the upstream catalyst is diagnosed based on the output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor, and the catalyst of the upstream side catalyst and the downstream catalyst Fuel ratio sensor and the output signal of the third air-fuel ratio sensor, and diagnoses of the upstream catalyst and the catalytic device are performed in different operation regions.

[Effect] Although the exhaust gas purifying apparatus having a plurality of catalysts, the correlation between the output signals of the air-fuel ratio sensors before and after each catalyst is examined by examining the respective catalysts in different operating regions, Enabling diagnosis.

Description

Diagnostic device of exhaust gas purification device for internal combustion engine

The present invention relates to an apparatus for diagnosing an exhaust gas purifying apparatus for an internal combustion engine using a plurality of catalytic converters arranged in series and more particularly to a system for diagnosing an exhaust gas purifying apparatus for an internal combustion engine using a plurality of air- To a diagnostic apparatus for an exhaust gas purifying apparatus for an internal combustion engine.

An apparatus for purifying the combustion exhaust gas of an internal combustion engine generally comprises a catalytic converter and an air-fuel ratio feedback control device. The catalytic converter is installed in the exhaust pipe to remove harmful components contained in the exhaust gas, particularly, HC, NOx and CO. The air-fuel ratio feedback control device needs to maintain the air-fuel ratio at a constant level in order to sufficiently exhibit the function of the catalytic converter Therefore, an air-fuel ratio sensor or an oxygen sensor is provided upstream of the catalytic converter in the exhaust pipe section to obtain the air-fuel ratio, and the fuel supply amount is controlled based on the air-fuel ratio.

However, the three-way catalyst used in the catalytic converter is a catalyst which is used in accordance with a change in the number of years of use, for example, impurities adhere to the catalytic portion of the catalytic converter by injecting the gasoline into the internal combustion engine, There has been a problem that performance deterioration occurs even within the period.

With respect to such a problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 63-97852, there is provided a second exhaust sensor for detecting the oxygen concentration on the downstream side of the catalytic converter installed in the exhaust system of the internal combustion engine, It is proposed to determine the deterioration of the catalytic action of the catalytic converter by the number of times of output inversion in the air-fuel ratio feedback control using the exhaust sensor. This is because, when the catalytic action deteriorates, the deterioration of the catalyst is judged indirectly by focusing on the fact that the oxygen concentration on the downstream side of the catalyst is substantially the same as the upstream side due to the decrease in the oxygen occlusion capability.

As a conventional technique relating to a plurality of catalysts arranged in series, Japanese Patent Application Laid-Open No. 5-26032 can be used. In this prior art, a system in which a second exhaust sensor is provided at an intermediate portion of the upstream and downstream catalytic converters in the exhaust system and a third exhaust sensor is provided at the downstream side of the downstream catalyst, The deterioration judgment of the upstream catalyst is carried out by the number of times of reversal of the second exhaust sensor under the air-fuel ratio feedback control based on the exhaust sensor. Further, the air-fuel ratio feedback control is performed based on the second exhaust sensor, and the deterioration judgment of the downstream catalyst is carried out by the number of times of reversal of the third exhaust sensor.

However, in the case where a plurality of catalytic converters are provided in the above-described conventional exhaust passage, if the exhaust sensor is provided downstream of the downstream catalytic converter and the deterioration of the catalyst is judged based on the output fluctuation, There is a problem.

In other words, since the atmosphere of the combustion exhaust gas acting on the upstream-side and downstream-side catalytic converters is different from each other, the degrees of deterioration of the respective catalytic converters are also different and it is difficult to maintain the reliability.

On the other hand, it is conceivable to provide an exhaust sensor for judging the deterioration of the upstream catalyst in the intermediate portion of the upstream and downstream catalytic converters in the exhaust passage. However, in the case where the catalytic converter alone is used, The oxygen partial pressure in the combustion exhaust gas downstream of the catalytic converter on the downstream side is unlikely to fluctuate extremely when the air-fuel ratio feedback control is performed based on the exhaust sensor upstream of the upstream catalytic converter, Therefore, there is a problem that the output of the exhaust sensor downstream of the downstream catalytic converter does not change unless the catalytic ability is extremely deteriorated, and in particular, the accuracy of the downstream catalytic converter deterioration determination is lowered.

Fuel ratio feedback is performed based on an exhaust sensor provided at an intermediate portion of upstream and downstream catalysts to solve such a problem. However, since engine control parameters and the like are forcibly changed for diagnosing deterioration of the catalyst, It is necessary to consider the occurrence of a new problem such as the influence of the influence.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine having a plurality of catalysts in which an air-fuel ratio sensor is provided before and after each catalyst, The present invention is to provide a system capable of individually diagnosing each catalyst by conducting the respective catalyst diagnosis by examining the correlation of the output signals and conducting the respective diagnoses in different operating regions.

In order to achieve the above object, an apparatus for diagnosing an exhaust gas purifying apparatus of an internal combustion engine according to the present invention includes means for detecting an operating state of an internal combustion engine, air-fuel ratio control means for adjusting the fuel injection amount so as to maintain the air- A first air-fuel ratio sensor provided in the exhaust passage of the internal combustion engine and provided with a plurality of exhaust gas-purifying catalysts and disposed upstream of the upstream catalyst in the exhaust passage, and a second air-fuel ratio sensor disposed downstream of the upstream catalyst and the exhaust passage A third air-fuel ratio sensor provided downstream of the downstream catalyst, and a diagnosis for diagnosing the upstream catalyst on the basis of output signals of the first air-fuel ratio sensor and the second air-fuel ratio sensor Fuel ratio sensor based on output signals from the first air-fuel-ratio sensor and the third air-fuel ratio sensor; and a diagnosis device that diagnoses the catalytic device in which the upstream catalyst and the downstream- And the diagnosis information of the catalyst on the downstream side of the exhaust passage, that is, the diagnosis information of the catalyst on the upstream side of the exhaust passage, and the diagnosis information of the catalyst on the upstream side of the exhaust passage, And means for estimating the degree of deterioration of the catalyst on the downstream side of the exhaust passage from the data map in which the diagnosis information of the catalytic device is taken as a lattice axis.

Further, the internal combustion engine operating region for diagnosing the upstream catalyst in the exhaust path and the internal combustion engine operating region for diagnosing the catalytic converter are different regions, Thereby diagnosing the catalytic device.

Fuel ratio sensor and the output signal of the third air-fuel ratio sensor and the output signal of the third air-fuel ratio sensor when the difference between the upstream catalyst of the exhaust passage and the purifying capability of the downstream catalyst of the exhaust passage is equal to or greater than a predetermined value, And the downstream catalyst is diagnosed on the basis of the output state of the downstream catalyst and the downstream catalyst.

The catalyst diagnosis method of the diagnostic apparatus of the exhaust gas purifying apparatus of the internal combustion engine according to the present invention constructed as described above is carried out by using a correlation method for obtaining correlation between output signals of the air-fuel ratio sensors before and after the catalyst, Fuel ratio is reduced at the downstream side of the catalytic device due to the oxidation and reduction action of the catalyst and the movement of the detection signal of the downstream air-fuel ratio sensor is also reduced. On the other hand, when the catalytic device starts to deteriorate, The movement starts to approach the upstream movement. The catalyst deterioration is diagnosed based on the similarity of the air-fuel ratio movement before and after the catalytic converter.

As a value indicating the similarity of the air-fuel ratios before and after the catalytic converter, a cross-correlation function of detection signals of the air-fuel ratio sensors before and after the catalytic converter is obtained. It is known that the correlation function is a known function in algebra and can be applied to the evaluation of signal similarity. If the similarity of the air-fuel ratio movements before and after the catalytic converter, that is, the similarity of the output signals of the air-fuel ratio sensors before and after the catalytic converter, is high, the correlation function shows a large value, and if the similarity is low, the correlation function shows a small value.

Fuel ratio sensor and the output signal of the second air-fuel ratio sensor is calculated by a correlation function calculation based on a correlation method to perform the deterioration diagnosis of the upstream catalyst. Also, the correlation function calculating means calculates the correlation function value between the first air-fuel ratio sensor and the third air-fuel ratio sensor, and performs deterioration diagnosis of the catalytic device including the upstream catalyst and the downstream catalyst.

The calculation of each correlation function is performed from the time when the operating state of the internal combustion engine enters the catalyst diagnosis region by the determination of the catalyst diagnosis region.

Further, in the diagnostic apparatus for an internal combustion engine exhaust gas purifying apparatus according to the present invention, a bypass passage for bypassing the upstream catalyst and a bypass valve for converting the flow of the exhaust gas between the upstream catalyst and the bypass passage side are provided, By providing the second air-fuel ratio sensor upstream or downstream of the outlet of the by-pass passage, it is possible to solve the problem of lowering the reliability of diagnosis in the diagnosis of the downstream catalyst and to make individual diagnosis of the upstream- do.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a basic configuration diagram of a diagnostic apparatus of an exhaust gas purifying apparatus of an internal combustion engine according to the present invention.

In the system of the present embodiment, the amount of intake air passing through the air cleaner and the throttle valve (not shown) and passing through the throttle sensor 2 for detecting the throttle angle is measured by the air flow sensor 1. The control device 3 of the internal combustion engine calculates an appropriate fuel injection amount by means of a measured value of the air flow sensor 1 or a rotation sensor (not shown) or the like, Control the organ.

The mixture of air and fuel thus measured and calculated is introduced into the combustion chamber of the internal combustion engine E through the intake manifold 5 and subjected to compression, explosion, and expansion strokes of the internal combustion engine E. And then exhausted. The first air-fuel ratio sensor 6 is installed in the exhaust manifold 5 'or immediately after the exhaust manifold 5' in order to know the oxygen concentration in the exhaust gas, and the detection of the first air-fuel ratio sensor 6 And corrects the fuel injection amount from the injector 4 based on the signal. In the system of the present embodiment, the upstream catalyst 9 and the downstream catalyst 10, which are arranged in series as purifying means for the combustion exhaust gas, are provided to constitute a catalytic device.

Further, a second air-fuel ratio sensor 7 is provided on the downstream side of the upstream catalyst 9 and a third air-fuel ratio sensor 8 is provided on the downstream side of the downstream catalyst 10. [ In the present embodiment, the oxygen sensor is used as the air-fuel ratio sensor, but another air-fuel ratio sensor may be used.

Each part of the catalyst diagnosis unit 11 of the system of this embodiment will be described. First, the configuration of the catalyst diagnosis unit 11 for diagnosing the catalytic device will be described. The catalyst diagnosis section 11 includes a catalyst diagnosis region determination means 12 for determining whether or not it is a region for diagnosing the catalytic device according to the value of each engine parameter, a signal detection means for detecting a signal of the first air-fuel ratio sensor 6, Fuel ratio sensor 7 and the signal of the third air-fuel ratio sensor 8, a correlation function calculating means 14 for calculating a correlation function between the signal of the first air-fuel ratio sensor 6 and the signal of the third air-fuel ratio sensor 8, The downstream side catalyst diagnosis means 15 that performs diagnosis of the downstream catalyst 10 on the basis of the calculation results of the correlation function calculation means 13 and the correlation function calculation means 14, Based on the results of the function calculating means 13 and the downstream catalyst diagnosis means 15, the deterioration determining means 16 for diagnosing the upstream catalyst 9, the downstream catalyst 10 and the overall catalyst device .

The catalyst diagnosis area judging means 12, the downstream catalyst diagnosis means 15 and the deterioration judgment means 16 are connected to the microcomputer programmed to realize the operations of the respective means described later in detail or the flow chart thereof .

An example of the correlation function is calculated by the following equation.

Therefore, the correlation function calculating means 13 is realized by performing the calculation of the above equation with the signal of the air-fuel ratio sensor 6 as X and the signal of the air-fuel ratio sensor 7 as Y. Further, the correlation function calculating means 14 is realized by performing the calculation of the above expression with the signal of the air-fuel ratio sensor 6 as X and the signal of the air-fuel ratio sensor 8 as Y. For example, the calculation of each correlation function is realized by a microcomputer programmed to calculate the above equation.

Although not shown, the catalyst diagnosis unit 11 includes a signal processing circuit for processing signals of the air-fuel ratio sensors 6, 7, and 8. [ The signal processing circuit is constituted by, for example, a band-pass filter for extracting a specific frequency component of a signal of the air-fuel ratio sensor 6, 7, 8.

Although not shown, the catalyst diagnosis unit 11 includes a failure occurrence display means for informing the driver of the occurrence of a failure when it is determined by the deterioration determination means 16 that the catalyst apparatus is faulty. The failure occurrence display means is realized, for example, by lighting the failure occurrence lamp (MIL) when the deterioration determination means (16) determines that the catalytic device is faulty.

Although not shown, the catalyst diagnosis unit 11 includes a memory for storing and storing diagnosis results of the catalytic device, and stores the results of determination by the degradation determination unit 16 in a memory. The memory is preferably a nonvolatile memory, and can be realized, for example, by a RAM having a backup power supply, or an EEPROM. In the event of a failure of the catalytic device, the service engineer can read the diagnostic results stored in the memory with a tester or the like for reference.

By using the above-described configuration and the catalyst diagnosis unit 11 according to the example of the realization method, the diagnostic means of the present catalyst apparatus is realized. In addition, the catalyst diagnosis unit 11 can be configured in an engine control unit including the internal combustion engine control device 3, or can be configured as a separate entity from the engine control unit.

The operation of each means constituting the catalyst diagnosis unit 11 will be described.

First, a signal indicating the operating state of the internal combustion engine is input to the catalyst diagnosis region determining means 12, and it is determined whether or not the operating state is an area suitable for the catalyst diagnosis.

The catalyst diagnosis of the catalytic apparatus in this embodiment uses a correlation method for obtaining a correlation function of the output signal of the air-fuel ratio sensor before and after the catalyst. That is, if the upstream catalyst 9 or the downstream catalyst 10 is not deteriorated, the movement of the air-fuel ratio becomes smaller downstream of the catalytic device due to the oxidation / reduction action of the catalyst, The motion of the signal is also reduced. On the other hand, when the catalyst device starts to deteriorate, the movement of the downstream air-fuel ratio begins to approach the upstream movement. The catalyst deterioration is diagnosed based on the similarity of the motion of the air-fuel ratios before and after the catalytic converter.

As a value indicating the similarity of the air-fuel ratios before and after the catalytic converter, a cross-correlation function of detection signals of the air-fuel ratio sensors before and after the catalytic converter is obtained. If the similarity of the air-fuel ratio movements before and after the catalytic converter, that is, the similarity of the output signals of the air-fuel ratio sensors before and after the catalytic converter, is high, the correlation function exhibits a large value, and if the similarity is low, the correlation function exhibits a small value.

Further, if the value indicates the similarity of the air-fuel ratio movement before and after the catalytic converter, it can be used as a value indicating the degree of deterioration even if it is a value other than the cross-correlation function.

The correlation function calculating means 13 based on the correlation method calculates the correlation function value between the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7 and performs the deterioration diagnosis of the upstream catalyst 9 . The correlation function calculating means 14 calculates a correlation function value between the first air-fuel ratio sensor 6 and the third air-fuel ratio sensor 8 and calculates the correlation function value between the upstream catalyst 9 and the downstream catalyst 10, The deterioration diagnosis is performed.

The calculation of each correlation function is performed after it is determined that the operation state of the internal combustion engine is entered into the catalyst diagnosis region by the catalyst diagnosis region determination means 12. [ Conditions for diagnosing include conditions such as at least the number of revolutions of the internal combustion engine, the load, the amount of intake air, the air-fuel ratio feedback condition, and the catalyst temperature.

Although not shown in FIG. 1, the correlation function calculating means 13 and the correlation function calculating means 14 are provided at least for sampling the output signals of the air-fuel ratio sensors 6, 7 and 8 and the means for sampling the air- 7, and 8, respectively.

The downstream catalytic diagnostic means 15 estimates the degree of deterioration of the downstream catalyst 10 based on the diagnosis result of the upstream catalyst 9 and the diagnosis result of the catalytic device. As a method for estimating the degree of deterioration of the downstream catalyst 10, a method of estimating the degree of deterioration of the downstream catalyst 10 is a method of estimating the degree of deterioration of the downstream catalyst 10, .

Each of the calculated correlation function values is input to the deterioration determination means 16, and when it is compared with a predetermined deterioration determination level for each catalyst, the determination is made as deterioration of the catalyst. The deterioration judging means 16 inputs the operating state at the time of diagnosis and corrects the judgment result based on the operating state. Further, when the result of the determination is stored and it is determined that the catalyst device is deteriorated, for example, the display lamp is turned on to notify the driver of the failure of the catalyst.

The feature of the diagnostic system according to the present embodiment is that the correlation function arithmetic operation is not performed at the same time but in different operation regions. For example, the diagnosis of the upstream-side catalyst 9 is performed to some extent under a low load operating range, and the diagnosis of the catalytic device is performed under a high load operating range. By performing the diagnosis in such a different operation region, the most suitable diagnosis condition can be given to each catalyst.

FIG. 2 is a control flow chart of the diagnostic system in the present embodiment, and will be described below with reference to FIG. 2.

When the internal combustion engine is started, the control device 3 is activated to start the control. When the program is started, it is first determined in step S201 whether or not an operation region for diagnosis of the upstream catalyst 9 is established , The process proceeds to step S202 where the correlation function calculation unit 13 calculates the correlation function based on the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7 in step S202.

If step S201 is not established, the process proceeds to step S203 to determine whether or not the operating region for the catalytic system diagnosis is established by the catalyst function calculating means 12. If the operating region is established, the flow advances to step S204 to perform the correlation function calculation by the correlation function calculating means 14 based on the output signals of the first air-fuel ratio sensor 6 and the third air-fuel ratio sensor 8. [

If the operation region of the diagnosis of the catalytic device is not established in step S203, the process returns to the start in step S210, and the program is restarted.

When the diagnosis of the upstream catalyst 9 and the diagnosis of the pre-catalyst device are completed, the process again proceeds to step S205, where the diagnostic results of the diagnosis of the upstream catalyst 9 and the diagnosis of the pre- The degree of deterioration of the downstream catalyst is estimated from the data map in which the diagnosis results of the upstream catalyst and the diagnosis results of the catalytic device are taken as grid axes.

Further, the process proceeds to step S206, and in step S206, the three individual diagnosis results and the downstream side catalyst deterioration degree estimates are stored, and the process proceeds to step S207.

In step S207, the diagnosis result of the upstream catalyst 9, the diagnosis result of the catalytic device, and the downstream catalyst deterioration estimates are compared with a predetermined deterioration determination level corresponding to each. When the diagnosis result of any one of the catalysts exceeds the determination level, it is determined in step S208 that the catalyst is deteriorated, and the process proceeds to step S209. In step S209, the driver is notified that the catalyst is deteriorating.

If the diagnosis result of any of the catalysts does not exceed the determination level in step S207, the process returns to step S210 to return to the start, and restarts the program.

The diagnosis system shown in FIG. 3 is an example of the case where there is a difference in purifying capability between the upstream catalyst 9 and the downstream catalyst 10 (for example, when the downstream catalyst 10 is larger than the upstream catalyst) Fuel ratio sensor 8 as a diagnostic method of the downstream catalyst, or the correlation between the output signals of the second air-fuel ratio sensor 7 and the third air-fuel ratio sensor 8 ) Can be diagnosed based on the correlation between the output signals of the respective sensors. Also in this diagnostic system, the diagnostic method of the diagnostic system shown in Fig. 1 can be applied. However, in this diagnosis system, since the diagnosis of the downstream catalyst 10 can be made directly, the downstream catalyst diagnosis means 15 is not necessary and the map for estimating the degree of deterioration of the downstream catalyst 10 becomes unnecessary. If it is necessary to know the deterioration state of the catalytic device, it may be estimated from the diagnosis results of the upstream catalyst 9 and the downstream catalyst 10, respectively. For example, a diagnosis result of the upstream catalyst 9 and a diagnosis result of the downstream catalyst 10 are estimated by providing a deterioration state map of the catalytic device with the lattice axis.

In the diagnostic system shown in Figs. 1 and 3, when the correlation value of the air-fuel ratio sensors 6, 7 before and after the upstream catalyst exceeds a predetermined value, the air-fuel ratio feedback control Fuel ratio feedback control based on the output signal of the air-fuel ratio sensor 7. The air-

FIG. 4 is a diagnostic system diagram of another embodiment of the present invention. A major difference from the diagnostic system of the first embodiment shown in FIG. 1 is that the bypass valve 17 and the bypass passage 18 are provided to bypass the exhaust gas to the downstream catalyst, The same members as those of the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

In the diagnostic system of the present embodiment, when diagnosing the downstream catalyst 10, the bypass valve 17 is opened so that the entire exhaust gas passes through the downstream catalyst 10 through the bypass passage 18. [ By doing so, the diagnosis of the downstream catalyst 10 can be carried out in the same manner as the diagnosis of the single catalyst. However, as the diagnosis condition of the downstream catalyst 10, it is necessary to perform the diagnosis under conditions such that the downstream catalyst 10 is sufficiently activated or the exhaust does not deteriorate. In FIG. 4, the second air-fuel ratio sensor 7 is provided at a position upstream of the outlet of the bypass passage 18, but may be provided at a downstream position.

The control of opening the bypass valve 17 not only for diagnosis but also for protecting the upstream catalyst 9 against high temperature in a particularly high rotation and high load operation is also included in the diagnosis system of this embodiment .

The diagnosis of the upstream catalyst 9 is made based on the correlation between the output signals of the first air-fuel ratio sensor 6 and the second air-fuel ratio sensor 7, While diagnosing the downstream catalyst 10, the diagnosis is made based on the correlation between the output signals of the first air-fuel ratio sensor 6 and the third air-fuel ratio sensor 8, while the second air-fuel ratio sensor 7 is diagnosed on the bypass path Fuel ratio sensor 7 and the output signal of the third air-fuel ratio sensor 8 when it is installed at a position downstream of the first air-fuel ratio sensor 18, When the diagnosis is made based on the correlation between the output signals of the second air-fuel ratio sensor 7 and the third air-fuel ratio sensor 8, since the second air-fuel ratio sensor 7 is disposed close to the downstream-side catalyst 10, Since the detection time delay of the air-fuel ratio sensors 7, 8 is reduced, a more accurate correlation can be obtained.

FIG. 5 is a control flow chart in the diagnostic system of the present embodiment, and will be described with reference to FIG. 5 below.

When the internal combustion engine is started, the control device 3 is activated to start the control. When the program is started, it is first determined in step S401 whether or not the diagnosis area of the upstream catalyst 9 is established, 12, it is determined whether or not the current operating state has entered the diagnostic region of the upstream catalyst 9. If YES, the process proceeds to step S402. In step S402, it is determined whether or not the bypass valve 17 is turned off, that is, the bypass passage 18 is closed. If the bypass valve 17 is closed, the flow advances to step S404. On the other hand, when the bypass passage 18 is open, the process proceeds to step S403, and in step 403, the bypass valve 17 is turned off to close the bypass passage 18 during the diagnosis, The process proceeds to S404.

In step S404, the correlation function between the output signals of the first and second air-fuel ratio sensors 6, 7 disposed before and after the upstream catalyst 9 is calculated. On the other hand, if it is determined in step S401 that the current operating state does not fall into the diagnostic region of the upstream catalyst 9, the process advances to step S405, and if it is determined in step S405 that it is in the diagnostic area of the downstream catalyst 10 . If the diagnosis area of the downstream catalyst 10 is established, the flow advances to step S406 to determine whether the bypass valve 17 is on, that is, whether the bypass passage 18 is open. If the bypass valve 17 is turned off, the process advances to step S407. In step S407, the bypass valve 17 is turned on to open the bypass passage 18 during the diagnosis, and then, in step S408 . In step S408, a correlation function between the output signals of the first and third air-fuel ratio sensors 6, 8 or the second and third air-fuel ratio sensors 7, 8 is calculated.

Further, the correlation function value of any one of the catalysts calculated in step S404 or S408 is compared with a predetermined deterioration determination level in step S409. If the correlation function value exceeds the deterioration determination level, it is determined that the catalyst is deteriorated. In step S410, the deterioration is indicated and the driver is informed that the catalyst is degraded, for example, by lamp lighting.

If it is determined in step S405 that the diagnosis operation area of the downstream catalyst 10 is not established, the process returns to step S412 to restart the program.

The determination result is stored in the memory in step S411. According to this embodiment, individual catalysts (that is, the upstream catalyst 9 and the downstream catalyst 10) can be treated in the same manner as the single catalyst, so individual diagnosis can be facilitated.

As can be understood from the above description, the diagnostic apparatus for an exhaust gas purifying apparatus of an internal combustion engine according to the present invention is not limited to the exhaust gas purifying apparatus having a plurality of catalysts, and the correlation between the output signals of the air- Of the catalysts in the different operating regions to diagnose individual catalysts, thereby enabling individual diagnosis of each catalyst.

FIG. 1 is a basic configuration diagram of a diagnostic apparatus of an exhaust gas purifying apparatus according to an embodiment of the present invention;

FIG. 2 shows a control flow chart of the embodiment shown in FIG. 1,

FIG. 3 is a view showing a configuration in which the catalyst diagnosis unit of the diagnostic apparatus of the exhaust gas purifying apparatus of the embodiment shown in FIG.

4 is a configuration diagram of a diagnostic apparatus of an exhaust gas purifying apparatus according to another embodiment of the present invention;

FIG. 5 is a control flow chart of another embodiment shown in FIG. 4.

DESCRIPTION OF THE REFERENCE NUMERALS

1: air flow sensor 2: throttle sensor

3: Internal combustion engine control device 4: Injector

5: intake manifold 6: first air-fuel ratio sensor

7: second air-fuel ratio sensor 8: third air-fuel ratio sensor

9: upstream catalyst 10: downstream catalyst

11: catalyst diagnosis unit 12: diagnosis area determination means

13: Correlation function calculation means 14: Correlation function calculation means

15: downstream-side catalyst diagnosis means 16: catalyst deterioration determination means

17: Bypass valve 18: Bypass passage

Claims (12)

Fuel ratio control means for controlling the fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas of the internal combustion engine at a predetermined value in response to the detected operating state, A first exhaust gas catalyst unit disposed upstream of the exhaust gas passage of the internal combustion engine; and a second exhaust gas catalyst unit disposed downstream of the exhaust gas passage, A first air-fuel ratio sensor located on the upstream side of the first unit in the exhaust gas passage; A second air-fuel ratio sensor located between the first unit and the second unit in the exhaust passage; A third air-fuel ratio sensor located on the downstream side of the second unit within the exhaust gas passage; First diagnostic means for diagnosing said first unit based on output signals from said first and second air-fuel ratio sensors; And second diagnostic means for diagnosing an engagement unit of the first unit and the second unit based on output signals from the first and third air-fuel ratio sensors, Wherein the first diagnosis means is configured to diagnose the first unit under a first operation region of the internal combustion engine, and the second diagnosis means is configured to diagnose the first unit when the load of the internal combustion engine is lower than the first operation region, And the diagnosis unit diagnoses the combined unit. The method according to claim 1, And third diagnostic means for diagnosing the second unit based on diagnostic information from the first diagnostic means for the first unit and diagnostic information from the second diagnostic means for the combination unit Wherein the exhaust gas purifying apparatus is provided with an exhaust gas purifying apparatus for an internal combustion engine. 3. The method of claim 2, The third diagnosis means uses the diagnosis information from the first diagnosis means for the first unit and the diagnosis information from the second diagnosis means for the combination unit as two variables on the rectangular coordinate system And means for estimating the degree of deterioration of said second unit with reference to a data map. The method according to claim 1, Wherein the purifying capacity of the second unit is larger than a purge capacity of the first unit by a predetermined amount or more, and the diagnostic apparatus further comprises an output signal from the first and third air-fuel ratio sensors and / Further comprising third diagnosing means for diagnosing said second unit based on the signal detected by said detecting means. The method according to claim 1, Wherein the first diagnostic means includes first correlation function calculation means for calculating a correlation function between output signals from the first and second air-fuel ratio sensors, Fuel ratio sensor and the second diagnostic means includes second correlation function calculation means for calculating a correlation function between output signals from the first and third air-fuel ratio sensors. The method according to claim 1, Further comprising: means for notifying a result of the diagnosis; and means for storing the diagnosis result. Fuel ratio control means for controlling the fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas of the internal combustion engine at a predetermined value in response to the detected operation state, A first exhaust gas purifying unit disposed upstream of the exhaust gas passage of the internal combustion engine; and a second exhaust gas purifying unit disposed downstream of the exhaust gas purifying unit, A bypass passage configured to bypass the first unit; A bypass valve configured to convert the exhaust gas flow between the first unit and the bypass passage; A first air-fuel ratio sensor located upstream of the bypass valve; A second air-fuel ratio sensor located at one of an upstream side and a downstream side of an outlet of the bypass passage in the exhaust gas passage; A third air-fuel ratio sensor located on the downstream side of the second unit within the exhaust gas passage; Fuel ratio sensor for detecting the first catalyst unit based on output signals from the first and second air-fuel ratio sensors when the bypass valve is switched to block the bypass passage and the exhaust gas flows through the first unit 1 diagnostic means; Wherein the bypass valve is switched to open the bypass passage, and when the exhaust gas flows through the bypass passage, output signals from the first and third air-fuel ratio sensors and the second and third air- And second diagnostic means for diagnosing the second catalyst unit based on one of the output signals of the second catalyst unit, Wherein the first diagnosis means is configured to diagnose the first unit under a first operation region of the internal combustion engine, and the second diagnosis means is configured to diagnose the first unit when the load of the internal combustion engine is lower than the first operation region, And diagnose the second unit based on a result of the determination by the determination unit. 8. The method of claim 7, Further comprising: means for notifying a result of the diagnosis; and means for storing the diagnosis result. Fuel ratio control means for controlling the fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas of the internal combustion engine at a predetermined value in response to the detected operating state, A diagnosis apparatus for an exhaust gas purifying apparatus, comprising: a first exhaust gas purifying catalyst unit disposed on an upstream side of an exhaust gas passage of an internal combustion engine; and a second exhaust gas purifying catalyst unit disposed on a downstream side, A bypass passage configured to bypass the first catalyst unit; A bypass valve configured to convert the exhaust gas flow between the first catalyst unit and the bypass passage; A first air-fuel ratio sensor located upstream of the bypass valve; A second air-fuel ratio sensor located at one of an upstream side and a downstream side of an outlet of the bypass passage in the exhaust gas passage; A third air-fuel ratio sensor located on the downstream side of the second catalytic unit in the exhaust gas passage; The bypass valve is switched to open the bypass passage, and when the exhaust gas flows through the bypass passage, the second catalyst unit is diagnosed based on output signals from the first and third air-fuel ratio sensors And a second diagnosing device for diagnosing the exhaust gas purifying apparatus for an internal combustion engine. Fuel ratio control means for controlling the fuel injection amount so as to maintain the air-fuel ratio in the exhaust gas of the internal combustion engine at a predetermined value in response to the detected operating state, A first exhaust gas purifying catalyst unit disposed upstream of the exhaust gas passage of the internal combustion engine; and a second exhaust gas purifying catalyst unit disposed downstream of the exhaust gas purifying catalyst unit, A bypass passage configured to bypass the first catalyst unit; A bypass valve configured to convert the exhaust gas flow between the first catalyst unit and the bypass passage; A first air-fuel ratio sensor located upstream of the bypass valve; A second air-fuel ratio sensor located at one of an upstream side and a downstream side of an outlet of the bypass passage in the exhaust gas passage; A third air-fuel ratio sensor located on the downstream side of the second catalytic unit in the exhaust gas passage; Fuel ratio sensor for detecting the first catalyst unit based on output signals from the first and second air-fuel ratio sensors when the bypass valve is switched to block the bypass passage and the exhaust gas flows through the first unit 1 diagnostic device; The bypass valve is switched to open the bypass passage, and when the exhaust gas flows through the bypass passage, the second catalyst unit is diagnosed based on output signals from the first and third air-fuel ratio sensors And a second diagnosing device for diagnosing the exhaust gas purifying apparatus for an internal combustion engine. 11. The method of claim 10, Wherein the first diagnosis device is configured to diagnose the first catalyst unit under a first operation region of the internal combustion engine and the second diagnosis device is configured to detect the load of the internal combustion engine under a second operation region different from the first operation region And diagnose the second catalyst unit based on a result of the determination by the determination unit. 11. The method of claim 10, Wherein the first diagnosis apparatus is configured to diagnose the first catalyst unit under a first operation region of the internal combustion engine and the second diagnosis apparatus is configured to diagnose the first catalyst unit under a second operation region in which the load of the internal combustion engine is larger than the first operation region And diagnose the second catalyst unit based on a result of the determination by the determination unit.